1. Field of the Invention
The present invention relates generally to object inspection apparatus and is directed more particularly to such object inspection apparatus that utilizes a pick-up device such as a video camera to inspect the objects.
2. Description of the Prior Art
Presently, automatic devices have been proposed in replacement of the manual object inspection system requiring human vision as well as manipulation. In the automatic devices a photoelectric conversion sensor is used to detect the object, and the output signal therefrom is electronically processed. Many systems use a video camera having a pick-up element such as a CCD or the like, to detect the object to be inspected by receiving the reflected light emitted as a result of being irradiated by a light source. Then, a corresponding video signal is processed by an exclusive electronic circuitry from which the inspection of the object is conducted.
Such appearance inspection apparatus that replaces the human inspection of the object requires the sensing of a variety of elements such as, for example, the shape of the object, its dimension, flaws in its appearance, and any foreign particle adhered thereon or mixed therewith, etc.
Further, since there is a wide variation in the inspected objects, e.g. from flat board-like objects to cubical objects with severe unevenness, the object inspection device is not normally intended to sense the entire object. In general, it is necessary only to conduct the inspection of a specific site and one that is limited to a partial area of the object.
For example, in the case illustrated in FIG. 1, where the inspection is intended to check for cracks in the body portion of a transparent glass bottle 1 and for foreign particles mixed therein, inspection areas or zones 2 and 3, as shown by the dotted lines are determined. These zones 2 and 3 are thus the only necessary portions to be inspected, and the image signals from such portions can be electronically analyzed to detect a flaw or the like that exist.
The determination of such specific inspection zones 2 and 3 is expressed as providing inspection windows, the periphery of which may be masked. FIG. 2 shows one example thereof wherein a target screen 4 such as, for example, of the video camera (not shown) or the picture screen of a video monitor (not shown) is created. Within this target screen 4, the aforementioned specific inspection zones or the windows 2 and 3 are provided as shown in FIG. 2, and only the areas inside these windows 2 and 3 form the subject zones for the inspection of the bottle 1. After providing such windows 2 and 3, if the bottle 1 to be inspected is transported to appear at the position indicated within the dotted line in FIG. 2 and then picked up by the video camera, the inspection of the necessary portions of the bottle 1, in other words the inspection of only the windows 2 and 3, will be carried out.
There are various means to provide the windows 2 and 3. For instance, there can be located, between the video camera and the bottle 1 which is the inspected object, an opaque plate with apertures that correspond to the shapes of windows 2 and 3 to thereby physically provide windows 2 and 3; or means to electronically control the image signal from the video camera by horizontal and vertical coordinates in correspondence with the windows 2 and 3; or to electronically provide windows 2 and 3 by computer software. Where the windows are provided as above and only the portions within the windows are made as zones to be inspected it is essential that the inspected object must be sensed at a predetermined exact position.
For such purpose, when inspected objects are moved on the conveyer, in the production line, a separate position detection means must be provided by the prior art in order to detect whether or not the object that is to be inspected has arrived at such predetermined position of the window zones. As a practical example there was needed an arrangement formed of a light projector and a light receiving sensor to detect the position at which the inspected object crosses the light beam from the light projector. Therefore, the system becomes complicated which confines the range of application.